1. Field of the Invention
The present invention relates to an antenna coil for an IC card and to the method of manufacturing the same. More specifically, the present invention relates to an antenna coil for an IC card in which a circuit pattern layer of the antenna coil for the IC card is formed of an aluminum foil, as well as to the method of manufacturing the same. Here, the aluminum foil is not limited to a pure aluminum foil but it also includes an aluminum alloy foil.
2. Description of the Related Art
Recently, IC cards have been developed remarkably, and the use of the IC cards is widening to telephone cards, credit cards, pre-paid cards, cash cards, ID cards and card keys. As a base material for the conventional IC cards, resin film such as a polyimide film, a general purpose polyethylene terephthalate (PET) film or the like has been used. A copper foil or a high-purity aluminum foil is laminated on each side of the resin film and subjected to etching, whereby a circuit pattern layer of copper or aluminum is formed on a surface of the base material, providing an antenna coil for the IC card.
The process of etching the copper foil for forming the circuit pattern layer takes too much time, and therefore production efficiency is low. Further, after the etching process of the copper foil, an oxidizing reaction tends to occur at the surface of the copper foil, making instable the electrical resistance value of the surface of the circuit pattern.
When such a resin as described above is used as a base material of the antenna coil for IC cards and copper foils are to be laminated on both surfaces of the base material, it is necessary to attain electrical conduction between the circuit pattern layers of the copper foils formed on opposing surfaces of the base material. For this purpose, a plating layer of a through hole is formed between the circuit pattern layers of the copper foil, or printing with silver paste is performed. Such process steps lead to increased cost for manufacturing the antenna coil for IC cards and lowers production efficiency.
When a high-purity aluminum foil (having the purity of at least 99.8 mass %) is used as the material for forming the circuit pattern layer, superior oxidation resistance can be attained. Etching, however, takes longer time, resulting in low production efficiency. An IC card having the circuit pattern layer formed by using the high-purity aluminum foil is susceptible to possible disconnection of the circuit caused by emboss processing or imprinting such as inscription provided on the final product, thus reliability is not very high.
An object of the present invention is to provide an antenna coil for an IC card having superior processability and allowing higher efficiency of production.
The antenna coil for an IC card in accordance with the present invention includes a base material containing resin and having a thickness of at least 15 xcexcm and at most 70 xcexcm, and a circuit pattern layer formed on a surface of the base material and having the thickness of at least 7 xcexcm and at most 60 xcexcm formed of a foil containing aluminum of at least 97.5 mass % and at most 99.7 mass %.
In the antenna coil for an IC card in accordance with the present invention, the foil constituting the circuit pattern layer has low aluminum purity, and therefore etch rate to form the circuit pattern layer can be improved, and hence production efficiency can be improved. Further, as the circuit pattern layer contains aluminum of the limited purity as mentioned above, it is possible to maintain electrical resistance value of the surface stable over a long time. Thus, an antenna coil for an IC card having higher stability over a long period of time can be attained.
Preferably, in the antenna coil for an IC card in accordance with the present invention, the foil constituting the circuit pattern layer includes iron by at least 0.7 mass % and at most 1.8 mass %.
Here, as the aluminum foil constituting the circuit pattern layer contains iron by a limited content, it has such strength and elongation that lead to superior processability. Therefore, during the steps of manufacturing the antenna coil for an IC card or during emboss processing of the final product, possible tearing of the aluminum foil or disconnection of the circuits can be prevented. Further, as the etch rate for forming the circuit pattern layer can be improved, production efficiency can be improved.
Preferably, in the antenna coil for an IC card in accordance with the present invention, the aluminum foil constituting the circuit pattern layer contains silicon by at least 0.03 mass % and at most 0.5 mass %.
Preferably, in the antenna coil for an IC card in accordance with the present invention, the aluminum foil constituting the circuit pattern layer contains silicon by at least 0.03 mass % and at most 0.5 mass % and copper by at most 0.3 mass %.
The polyimide film used as the base material of the antenna coil for an IC card is expensive, and in addition it absorbs much moisture, resulting in variation in electrical characteristic of the antenna coil during use of the IC card, possibly causing a malfunction. When a general purpose PET film is used as the base material of the antenna coil for an IC card, there would be an undesirable shrinkage as the base material is heated when an IC chip is mounted on the surface of the circuit pattern layer, for example. Therefore, dimensional accuracy of the circuit pattern layer formed on the base material of general purpose PET file becomes instable, and in addition, smoothness of the base material deteriorates.
Therefore, it is preferred that the base material includes a resin of which thermal contraction when held at 150xc2x0 C. for 30 minutes is at most 0.3%.
Here, as the base material includes the resin having such a limited thermal contraction coefficient, contraction can be effectively prevented in the step of thermal processing at the time of mounting the IC chip, for example. Hence, dimensional accuracy of the circuit pattern layer can be maintained stable and the smoothness of the base material can also be maintained satisfactorily.
Preferably, the resin used as the base material of the antenna coil for an IC card in accordance with the present invention is at least one selected from the group consisting of low profile polyethylene terephthalate (PET) and low profile polyethylene naphthalate (PEN).
Preferably, in the antenna coil for an IC card in accordance with the present invention, the circuit pattern layer includes a first circuit pattern formed on one surface of the base material, and a second circuit pattern layer formed on the other surface of the base material. Here, it is preferred that at least a part of the first circuit pattern layer is in contact with at least a part of the second circuit pattern, penetrating through the base material. This enables electrical conduction between the first and second circuit pattern layers. Contact between the first and second circuit pattern layers can be attained easily by a crimping process.
Preferably, the antenna coil for an IC card in accordance with the present invention further includes an adhesive layer interposed between the circuit pattern layer and the base material for bonding therebetween. It is preferred that the adhesive layer includes a polyurethane based adhesive containing an epoxy resin.
There is a problem that when the manufactured antenna coils for the IC cards are stacked on one another or wound as a belt-shaped roll for shipping or storage, overlapping portions are adhered with each other (hereinafter referred to as blocking). Therefore, when an IC card is to be manufactured using the antenna coil, separation of the adhered portions of the antenna coils is expected to be difficult, possibly stopping the manufacturing line.
In order to prevent the blocking, excessive adhesive on the resin film as the base material should be removed, or a released paper should be inserted to overlapping portions of the antenna coil. Perfect removal of the adhesive is very difficult. When a releasing paper is inserted, an additional step of removing the release paper becomes necessary in the subsequent manufacturing process. Therefore, in either case, an additional process step is required, resulting in increased cost of manufacturing.
Therefore, it is preferred that the antenna coil for an IC card in accordance with the present invention further includes an underlying coating layer formed on the surface of the base material, inserted between the circuit pattern layer and the base material. As the underlying coating layer is provided on the surface of the base material, even when antenna coils are stacked on one another, the base materials on which circuit pattern layers are formed are not brought into tight adhesion, as the base materials are stacked with underlying coatings positioned therebetween. This prevents blocking. Accordingly, undesired stopping of the manufacturing line of the IC card can be prevented. Here, it is further preferred that the antenna coil for an IC card additionally includes an adhesive layer for bonding positioned between the underlying coating layer and the base material. The adhesive layer preferably includes a polyurethane based adhesive containing an epoxy resin.
Preferably, in the antenna coil for an IC card in accordance with the present invention, the thickness of the underlying coating layer is at least 0.1 xcexcm and at most 5 xcexcm.
More preferably, the underlying coating layer includes at least one selected from the group consisting of epoxy based primer, acrylic primer, and vinyl chloride-vinyl acetate copolymer based primer.
The method of manufacturing an antenna coil for an IC card in accordance with the present invention includes the following steps.
(a) On a surface of a base material containing a resin and having the thickness of at least 15 xcexcm and at most 70 xcexcm, fixing a foil having the thickness of at least 7 xcexcm and at most 60 xcexcm and containing aluminum of at least 97.5 mass % and at most 99.7 mass %, by using an adhesive.
(b) Printing a resist ink layer of a prescribed pattern on the foil.
(c) Etching the foil using the resist ink layer as a mask, to form a circuit pattern layer containing aluminum.
(d) After etching the foil, removing the resist ink layer.
In the method of manufacturing in accordance with the present invention, the circuit pattern layer is formed by using a foil having the limited thickness and containing aluminum of the limited purity as described above, and therefore the time for etching to form the pattern layer can be reduced. Therefore, it becomes possible to improve efficiency of production in manufacturing the antenna coils for IC cards.
Preferably, in the method of manufacturing an antenna coil for an IC card in accordance with the present invention, the step of fixing a foil includes fixing a foil on one surface and on the other surface of the base material. Preferably, the step of forming a circuit pattern layer includes the step of forming a first circuit pattern layer on one surface of the base material and forming a second circuit pattern layer on the other surface of the base material.
Preferably, the method of manufacturing an antenna coil for an IC card in accordance with the present invention further includes the step of bringing at least a part of the first circuit pattern layer into contact with at least a part of the second circuit pattern layer by a crimping process. Here, in order to establish electrical conduction between the first and second circuit pattern layers formed on opposing surfaces of the base material, it is possible to bring into contact at least parts of the first and second circuit pattern layers by the crimping process, and hence conduction can be established through a simple process step. Therefore, as compared with the conventional method of manufacturing, manufacturing cost can be reduced and production efficiency can be improved.
The method of manufacturing an antenna coil for an IC card in accordance with another aspect of the present invention includes the following steps.
(a) Forming an underlying coating layer on one surface of an aluminum foil.
(b) Fixing a base material containing a resin on a surface of the underlying coating layer.
(c) Printing a resist ink layer having a prescribed pattern on the other surface of the aluminum foil.
(d) Etching apart of the aluminum foil using the resist ink layer as a mask to form a circuit pattern layer.
(e) After etching the part of the aluminum foil, removing the resist ink layer.
Preferably, in the method of manufacturing an antenna coil for an IC card in accordance with the present invention, the step of fixing a base material on the surface of the underlying coating layer includes the step of fixing the base material on a surface of the underlying coating layer using a polyurethane based adhesive containing an epoxy resin.
Preferably, in the method of manufacturing an antenna coil for an IC card in accordance with the present invention, the step of fixing the base material includes adhering one surface of the base material onto a surface of the underlying coating layer formed on one surface of a first aluminum foil and adhering the other surface of the base material onto a surface of the underlying coating layer formed on one surface of a second aluminum foil, and the step of forming the circuit pattern layer includes forming the first circuit pattern layer by etching a part of the first aluminum foil on one surface of the base material and forming a second circuit pattern layer by etching a part of the second aluminum foil on the other surface of the base material. It is needless to say that the etching of a part of the first aluminum foil and etching of a part of the second aluminum foil may be performed simultaneously.
As described above, the antenna coil for an IC card in accordance with the present invention is suitable for mass production at a low cost with high efficiency, and has superior processability, dimensional accuracy, heat resistance, stability over time and practical strength. Therefore, the antenna coil can be provided as a component for an IC card that has high reliability and capable of exhibiting stable performance over a long period of time.
Further, the antenna coil for an IC card in accordance with the present invention ensures smooth pay off or supply leaf by leaf without blocking. Therefore, lowering of productivity in the subsequent step of the manufacturing line of the IC card can be prevented.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.